20 meters of snow, Japan road clearance

How do you clear 20 meters of snow? It may seem like an absurd question but in Japan every year snow plows are faced with this problem.
It happens in the mountains of the "Tateyama Route" where in spring the buses travel along a road set between 2 walls of snow up to 20 meters high. “The road of the snow walls” it is freed from the snow thanks to powerful bulldozers which in days and days of great work move enormous masses of snow obtaining a path immersed in white.